The variable length of the natural day at different seasons led in the very earliest times to the adoption of the civil day (or one revolution of the sun) as a standard of time. The Hebrews reckoned the day from evening to evening, (Leviticus 23:32) deriving it from (Genesis 1:5) "the evening and the morning were the first day." The Jews are supposed, like the modern Arabs, to have adopted from an early period minute specifications of the parts of the natural day, and you can find
more about that here on
st-takla.org on other commentaries and
dictionary entries. Roughly, indeed, they were content to divide it into "morning, evening and noonday," (Psalms 55:17) but when they wished for greater accuracy they pointed to six unequal parts, each of which was again subdivided. These are held to have been--

"the dawn."

"Sunrise."

"Heat of the day," about 9 o'clock.

"The two noons," (Genesis 43:16; 28:29)

"The cool (lit. wind) of the day," before sunset, (Genesis 3:8)--so called by the Persians to this day.

"Evening." Before the captivity the Jews divided the
night into three watches, (Psalms 63:6; 90:4) viz. the first watch, lasting till midnight, (Lamentations 2:19) the "middle watch," lasting till cockcrow, (Judges 7:19) and the "morning watch," lasting till sunrise. (Exodus 14:24) In the
New Testament we have allusions to four watches, a division borrowed from the Greeks and Romans. These were--

From twilight till 9 o/clock, (Mark 11:11; John 20:19)

Midnight, from 9 till 12 o'clock, (Mark 13:35) 3 Macc 5:23.

Till daybreak. (John 18:28) The word held to mean "hour" is first found in (Daniel 3:6,15; 5:5) Perhaps the Jews, like the Greeks, learned from the
Babylonians the division of the day into twelve parts. In our Lord's time the division was common. (John 11:9)